Preparation of fertilizer salts which are practically free of chlorine and sulfate



June 20, 1967 A. H. DE ROOIJ 3,325,667

PREPARATION OF FERTILIZER SALTS WHICH ARE PRACTICALLY FREE OF CHLORINEAND SULFATE Filed April 3, 1964 United States Patent PREPARATION OFfiE-RTILHZER SALTS WHICH ARE PRACTICALLY FREE OF CHLORINE AND SULFATEAbraham H. de Rooij, Geleen, Netherlands, assignor to Stamicarbon N.V.,Heerlen, Netherlands I Filed Apr. 3, 1964, Ser. No. 357,122

Claims priority, application Netherlands, Apr. 5, 1963,

5 Claims. (Cl. 71--39) The present invention relates to the preparationof fertilizer salts which are practically free of chlorine and sulfateand contain one or more plant nutrients from the group of potassium,ammonia nitrogen, magnesium, nitratenitrogen, and phosphorus inphosphate form, or of mixtures of such-salts,

The process is applied to solutions obtained by decomposition ofphosphate rock with an excessive amount with respect to the amount ofcalcium contained in the phosphate rock-of concentrated nitric acidhaving a nitric acid content of at least 40% by weight. To thesesolutions, sulfates of potassium, ammonia or magnesium, or mixtures ofthese sulfates, have been added to precipitate the calcium in the formof gypsum and to remove it from the solution. In some cases part of thecalcium has been separated from the solution prior to the addition ofsulfate, e.g. by crystallization or by extraction with an organicsolvent, as a result of which the amount of gypsum to be filtered oftlater-after the addition of sulfate-will be smaller. In this way asolution is obtained which, in addition to free nitric acid andphosphoric acid, contains the fertilizer salts referred to above.

The object of the present invention is to provide an efiicient method ofrecovering these fertilizer salts from the solutions referred to above,and, more specifically, the invention effects separation between thedissolved salts and the dissolved free acid-nitric acid andphosphoricacid. During this separation, nitrate contained in thesolution may also be converted into phosphate and free nitric acid bythe action of free phosphoric acid.

According to the invention, this separation, and the conversion, if any,is effected if the solution is subjected to an extraction with a lower,poorly water-miscible, aliphatic alcohol with 4-6 carbon atoms, such asbutyl alcohol, isobutyl alcohol, amyl alcohol, isoamyl alcohol ormixtures of such alcohols, as a result of which on the one hand thealiphatic alcohol and the nitric acid and phosphoric acid dissolved init, and on the other hand an aqueous solution of nitrates andphosphates, is obtained. Owing to the fact that the extraction agentpreferentially takes up nitric acid, the extraction will, depending onthe nature of the extraction agent and the volumetric ratio betweentheextraction agent and the solution to be extracted, usually be attendedwith a partial conversion of nitrate and phosphoric acid into thephosphate and nitric acid.

I The solution obtained in the.ext raction, which contains nitratesand/or phosphates, is stripped of extraction.

agent which has also been dissolved, and subsequently, by evaporationor, if so desired, by crystallization, processed to recover thecorresponding salts or salt mixtures. In the extraction the volumetricratio between the extraction agent and the solution to be extracted maybe varied widely. The extraction can, moreover, be carried out both as acontinuous process in extraction columns, and as a discontinuous processin stirring vessels.

To effect a good separation between the salts and the free acids, avolumetric ratio of at least '1 part by volume of extraction agent to 1part by volume of solution to be extracted is required; by preference, avolumetric ratio of 2.5 to 3.5 parts by volume of dry extraction agentto 1 3,326,667 Patented June 20, 1967 ice part by volume of solution tobe extracted will be used,

version of nitrate and phosphoric acid into phosphate and nitric acid.However, this conversion can be counteracted by extracting the solutionwith an extraction agent already containing nitric acid.

The conversion of nitrate and phosphoric acid into phosphate and nitricacid can be promoted by adding a lower aliphatic ketone to theextraction agent-consisting of lower aliphatic alcohols with 4 to 6carbon atoms or mixtures of these alcoholse.g. in the ratio of 2 partsby volume of alcohol to 1 part by volume of ketone. The application ofmethyl isobutyl ketone in particular, ensures not only a fairlycompleteconversion, but also a very selective separation between thesalts and the free acids in the extraction.

Conversions of solutions containing salts and acids according to theequation with simultaneous extraction of the resulting acid HX, with anorganic solvent, have been proposed before (see Belgian patentspecification No. 556,751).

In this known process dilute solutions containing salts and acids aresubjected to an extraction with an organic solvent. The present processdoes not relate to the extraction of dilute solutions containing saltsand acids 'with the aid of an organic solvent but to the extraction ofsolutions obtained by'decomposition of phosphate rock with an excessiveamountwith respect to the amount of calcium contained in the phosphaterockof relatively concentrated nitric acid having a nitric acid contentof at least 40% by weight.

It has been found that the organic extraction agent is resistant to theconcentrated phosphoric and nitric medium of the solutions to beextracted, even if the decomposition of the phosphate rock is effectedfor instance with %-by-weight nitric acid, provided the extractiontemperature is kept below 40 C.

' The process now will be described in detail with reference to theattached figure, which gives a diagrammatical representation of theprocess.

In the situation shown in the figure, the nitric decomposition liquor tobe processed after the decomposition of the phosphate rock is, fed viaconduit 1, to a reservoir 2, in which the solution is treated with asulfate, or

a mixture of sulfates, with conversion of the calcium Part of thismother liquor is separated ofi via conduit 8 to dissolve sulfate inreservoir 3. In extraction column 9 the solution is extracted with anorganic solvent which, via conduit 11, is fed from storage vessel 10 tothe base of column 9. Via conduit 12, a solution which has beenpractically completely freed from free acids and substantially consistsof nitrate and phosphate is discharged from the base of the extractioncolumn and fed to a stripping column 13, where the entrained organicsolvent is stripped off. The solution is then treated, in a neutralizer14, with NH supplied via conduit 15, to neutralize any free acid stillpresent, after that freed from water in evaporator 16, and finallygranulated to a fertilizer in a known way.

The organic solvent discharged from the top of extraction column 9,which solvent now contains nitric acid and phosphoric acid, is fed, viaconduit 17, to the base of a second extraction column 18, where it iswashed with a small amount of water, which is supplied from reservoir 19to the top of the said column. The purpose of this washing is to removeany entrained nitrate. The nitratecontaining water is fed back to thetop of extraction column 9 via conduit 20. The organic solventcontaining the free acids is supplied, via conduit 21, to a neutralizer22, there neutralized with NH supplied via conduit 23, and finally fedto a separator 24. The neutralization causes a phase separation,resulting in the formation of an upper layer consisting of organicsolvent, and a bottom layer consisting of a solution of the ammoniumsalts of nitric acid and phosphoric acid.

The upper layer is fed to the storage vessel 10 for the organic solventvia conduit 25; via conduit 26, the bottom layer is fed to a strippingcolumn 27, where the organic solvent residues are stripped off. The saltsolution is evaporated in device 28, and after that granulated to anN.P. fertilizer with 100%-water-solu ble phosphate in a known way.

The amounts of organic solvent discharged from the top of the strippingcolumns 13 and 27 are fed to storage vessel 10 via the conduits 30 and29, respectively. The water washing in the second extraction column canbe omitted if the organic solvent discharged from the top of extractioncolumn 9 is directly fed to neutralizer 22 via conduit 31. If, at thebeginning of the process, potassium sulfate has been used forprecipitating the gypsum, an N.P. fertilizer is then obtained whichcontains some potassium, but so little of it that this potassium has tobe regarded as lost; this drawback is offset, however, by the advantagethat less water has to be evaporated in evaporator 16.

The above-described extractions can be carried out in normal columnsfilled with packing bodies or in plate columns; by preference, theliquids are made to pulsate in the column.

Example 1 905 kg. of K 50 was added to 6000 kg. of solution which hadbeen obtained by decomposition of phosphate rock with nitric acid, andfrom which part of the dissolved calcium nitrate had been removed byextraction, as a result of which the solution contained 853 kg. of Ca(NO360 kg. of HNO and 1080 kg. of H PO in 3700 kg. of H 0. Consequently,705 kg. of CaSO /2 aq. could be filtered off.

The liquid filtered off (6200 kg), which contained 1050 kg. of KNO 1080kg. of H PO 360 kg. of HNO and 45 kg. of still dissolved gypsum, was fedto the top of column 9 together with 430 kg. of washing liquid, andextracted there with 13,100 kg. of hydrous butanol (1350 kg. of H Fromthe base of column 9, 4270 kg. of solution was I discharged, from which110 kg. of butanol was stripped oil? in stripping column 13; thesolution was neutralized with 31 kg. of NH in neutralizer 14. Afterevaporation 1400 kg. of fertilizer was obtained, which mainly consistedof 740 kg. of KNO 410 kg. of KH PO 211 kg. of NH H PO by the side of 45kg. of CaSO i.e. an N.P.K. fertilizer containing 9.2% by weight of N,24.5% by weight of P 0 34.5% by weight of K 0.

4 umn 18 was neutralized with 253 kg. of NH in neutralizer 22. Afterseparation of the butanol and the salt solution in separator 24,stripping off the still dissolved butanol, and evaporation in evaporator28, 1410 kg. of an N.P. fertilizer consisting of ammonium phosphate andammonium nitrate (21.2% by weight of N and 30.8% by weight of P 0 wasobtained.

Example 2 If the 6200 kg. of filtered-off liquid of Example 1 isintroduced into the top of column 9 together with 376 kg. of washingliquid, and there extracted with 13,000 kg. of a mixture of butanol,methyl isobutyl ketone and water, containing 1800 kg. of H 0 and 4000kg. of methyl isobutyl ketone, an amount of 5040 kg. of solution isobtained from the bottom of column 9, from which solution 100 kg. ofbutanol and 10 kg. of methyl isobutyl ketone are removed by stripping ina stripping column 13. After neutralization with 34 kg. of NH inneutralizer 14, followed by evaporation of the liquid, 1500 kg. ofN.P.K. fertilizer is obtained, consisting of 5550 kg. of KNO of KH2PO4,229 kg. of NH H PO kg. of CaSO i.e. an N.P.K. fertilizer with 7% byweight of N, 33% by weight of P 0 and 33% by weight of K 0.

If the liquid discharged from the bottom of column 9 is again extractedwith 9750 kg. of the mixture of butanol, methyl isobutyl ketone andwater, followed by stripping, neutralization and evaporation, an amountof 1315 kg. of N.P.K. fertilizer is eventually obtained, consisting of421 kg. of KNO 846 kg. of KH PO 2 Of NH4H2PO4, 45 kg. of CaSO i.e. anN.P.K. fertilizer containing 4.5% by weight of N, 33.7% by weight of P 037.2% by weight of K 0.

Example 3 Instead of 905 kg. of K 418 kg. of K 50 and 370 kg. of (NH SOwere now added to the starting solution used in Example 1. The gypsumformed was filtered off, and the solution freed from gypsum, whichsolution (6050 kg.) contained 480 kg. of KNO 440 kg.- of NH NO 1080 kg.of H PO 360 kg. of HNO and 46 kg. of still dissolved gypsum, wasextracted in column 9 with 20,000 kg. of nitric acid-containing butanolconsisting of 1400 kg. of HNO 3050 kg. of H 0, and 15,550 kg. ofbutanol. In this way a good separation was effected between the nitrateson the one hand, and the free acids on the other hand; from the base ofcolumn 9, 3770 kg. of solution was discharged, from which kg. of butanolwas stripped ofi; the solution was neutralized with 8.9 kg. Of NH3.

The neutralized solution was evaporated and yielded 910 kg. of afertilizer mixture mainly consisting of KNO and NH NO (22.8% by weightof N by the side of 23.5% by weight of K 0).

The butanol extract discharged from the top of column 9 was neutralizedwith 651 kg. of NH after separation of the butanol and the salt solutionin separator 24, stripping oif still dissolved butanol, and evaporation,about 3500 kg. of an N.P. fertilizer mainly consisting of ammoniumphosphate and ammonium nitrate (22% by weight of N and 22% by weight ofP 0 was obtained.

What is claimed is: 1. A process for producing from phosphate rockfertilizer salts which are practically free of chlorine and sulfate andwhich contain at least one plant nutrient selected from the groupconsisting of potassium, ammonia nitrogen, magnesium, nitrate nitrogenand phosphate, comprising (l) decomposing said phosphate rock with anexcessive amount of aqueous, concentrated nitric acid having a nitricacid content of at least 40% by weight, (2) adding to the resultantsolution of decomposed phosphate rock a sulfate of at least one memberof the group consisting of potassium, ammonia and magnesium to form (a)an aqueous solution of free nitric and phosphoric acid and nitrate andphosphate fertilizer salts having as their positive radical the cationof said added sulfate and (b) a precipitate of gypsum, (3) removing saidgypsum, (4) contacting said aqueous solution with at least one lower,poorly water-miscible, aliphatic alcohol which contains 4-6 carbon atomsto form an aqueous phase containing said aqueous solution and saidfertilizer salts, and an alcohol phase containing said free nitric andphosphoric acids, (5) separating said alcohol phase from said aqueousphase, (6) neutralizing said aqueous phase, and (7) recovering saidfertilizer salts therefrom.

2. A process according to claim 1, in which said alcohol contains, inadmixture therewith, at least one lower aliphatic ketone to increase theconversion of nitrates and phosphoric acid to nitric acid andphosphates.

3. A process according to claim 1 in which the fertilizer salts arerecovered from said aqueous phase by evaporation.

4. A process according to claim 1 in which there is used at least 1 partby volume of said alcohol for each part by volume of said aqueoussolution.

5. A process according to claim 1 including removing any alcohol fromsaid aqueous phase prior to recovering said fertilizer salts.

References Cited UNITED STATES PATENTS 1,981,145 11/1934 Keller 23-312 X2,880,063 3/1959 Baniel et al 23312 X 2,885,265 5/1959 Cunningham 23l652,914,380 11/1959 Vickery 23109 3,245,777 4/1966 Chang 7139 DONALL H.SYLVESTER, Primaly Examiner.

T. D. KILEY. Assistant Examiner.

1. A PROCESS FOR PRODUCING FROM PHOSPHATE ROCK FERTILIZER SALTS WHICHARE PRACTICALLY FREE OF CHLORINE AND SULFATE AND WHICH CONTAIN AT LEASTONE PLANT NUTRIENT SELECTED FROM THE GROUP CONSISTING OF POTASSIUM,AMMONIA NITROGEN, MAGNESIUM, NITRATE NITROGEN AND PHOSPHATE COMPRISING(1) DECOMPOSING SAID PHOSPHATE ROCK WITH AN EXCESSIVE AMOUNT OF AQUEOUS,CONCENTRATED NITRIC ACID HAVING A NITRIC ACID CONTENT OF AT LEAST 40% BYWEIGHT, (2) ADDING TO THE RESULTANT SOLUTION OF DECOMPOSED PHOSPHATEROCK A SULFATE OF AT LEAST ONE MEMBER OF THE GROUP CONSISTING OFPOTASSIUM, AMMONIA AND MAGNESIUM TO FORM (A) AN AQUEOUS SOLUTION OF FREENITRIC AND PHOSPHORIC ACID AND NITRATE AND PHOSPHATE FERTILIZER SALTSHAVING AS THEIR POSITIVE RADICAL THE CATION OF SAID ADDED SULFATE AND(B) A PRECIPITATE OF GYPSUM, (3) REMOVING SAID GYPSUM, (4) CONTACTINGSAID AQUEOUS SOLUTION WITH AT LEAST ONE LOWER, POORLY WATER-MISCIBLE,ALIPHATIC ALCOHOL WHICH CONTAINS 4-6 CARBON ATOMS TO FORM AN AQUEOUSPHASE CONTAINING SAID AQUEOUS SOLUTION AND SAID FERTILIZER SALTS, AND ANALCOHOL PHASE CONTAINING SAID FREE NITRIC AND PHOSPHORIC ACIDS, (5)SEPARATING SAID ALCOHOL PHASE FROM SAID AQUEOUS PHASE, (6) NEUTRALIZINGSAID AQUEOUS PHASE, AND (7) RECOVERING SAID FERTILIZER SALTS THEREFROM.